Re: [PATCH v2 2/2] tun: update file current position
On 12/06/2013 12:45 PM, David Miller wrote: > From: Zhi Yong Wu > Date: Fri, 6 Dec 2013 17:08:50 +0800 > >> From: Zhi Yong Wu >> >> Signed-off-by: Zhi Yong Wu > > Also applied and queued up for -stable, thanks. > > I noticed in these two cases that that min_t() adjustment of 'ret' > seems strange. I can't understand why it's needed. > > If, for example, tun_do_read() really did read more than 'len' > bytes: > > 1) That would write past the end of the buffer. > > 2) Writing a different value to the ->ki_pos would mean >that ->ki_pos is now inaccurate. > > Unless someone can explain why the min_t() is needed, we should remove > it. So, back when that code was added, it was actually possible for the tun_do_read to return a value larger then user specified length, but the copy would only be done the length bytes. This was used to signal MSG_TRUNC. Specifically we had the following code in tun_put_user() len = min_t(int, skb->len, len); skb_copy_datagram_const_iovec(skb, 0, iv, total, len); total += skb->len; This has since changed to: len = min_t(int, skb->len, len); ... skb_copy_datagram_const_iovec(skb, vlan_offset, iv, total, len); total += len; So, no it seems impossible to return a value larger then user specified length, so MSG_TRUNC will never be set. It probably makes sense to signal message truncation, but that seems broken right now. -vlad > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v2 2/2] tun: update file current position
From: Zhi Yong Wu Date: Sat, 7 Dec 2013 04:32:20 +0800 > If you hope to submit the patch for this, please let me know, thanks. Someone should :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH v2 2/2] tun: update file current position
On Sat, Dec 7, 2013 at 1:45 AM, David Miller wrote:
> From: Zhi Yong Wu
> Date: Fri, 6 Dec 2013 17:08:50 +0800
>
>> From: Zhi Yong Wu
>>
>> Signed-off-by: Zhi Yong Wu
>
> Also applied and queued up for -stable, thanks.
>
> I noticed in these two cases that that min_t() adjustment of 'ret'
> seems strange. I can't understand why it's needed.
>
> If, for example, tun_do_read() really did read more than 'len'
> bytes:
>
> 1) That would write past the end of the buffer.
>
> 2) Writing a different value to the ->ki_pos would mean
>that ->ki_pos is now inaccurate.
>
> Unless someone can explain why the min_t() is needed, we should remove
> it.
Yes, from my side, it seems to be impossible that ret is bigger than
let or total_len.
So we also remove the branch "if (ret > total_len) {...}" in xxx_rcvmsg().
If you hope to submit the patch for this, please let me know, thanks.
--
Regards,
Zhi Yong Wu
--
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Re: [PATCH v2 2/2] tun: update file current position
From: Zhi Yong Wu Date: Fri, 6 Dec 2013 17:08:50 +0800 > From: Zhi Yong Wu > > Signed-off-by: Zhi Yong Wu Also applied and queued up for -stable, thanks. I noticed in these two cases that that min_t() adjustment of 'ret' seems strange. I can't understand why it's needed. If, for example, tun_do_read() really did read more than 'len' bytes: 1) That would write past the end of the buffer. 2) Writing a different value to the ->ki_pos would mean that ->ki_pos is now inaccurate. Unless someone can explain why the min_t() is needed, we should remove it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
